Humans and most other organisms manifest circadian (daily) rhythms which are controlled by an endogenous biochemical oscillator. Many cellular processes, including cell division, enzyme activity, and gene expression are timed by this oscillator. These "biological clocks" are important to human physiology. For example, psychiatric and medical studies have shown that circadian rhythmicity is involved in some forms of depressive illness, "jet lag," drug tolerance/efficacy, memory and insomnia. Therefore, understanding the biochemical mechanism of circadian clocks may lead to procedures which will be useful in the diagnosis and treatment of disorders that are relevant to sleep, mental health, and pharmacology. Despite the importance of clocked phenomena, however, clues to the nature of the underlying biochemical mechanism are only just beginning to emerge. So far, these clues suggest that the mechanism may have important similarities in organisms as diverse as fungi, fruitflies, and mammals. However, we still do not know whether the circadian pacemaker depends upon a known metabolic pathway, or if it is driven by a totally unknown system. The biochemical mechanism of circadian oscillators is the most fundamental unanswered question in this field. Our approach will elucidate components of the molecular mechanisms of circadian clocks by using model systems that will allow specific technological approaches to this important question. We have found oscillations of the global cellular regulator, ionic calcium, and we will ascertain the role of these oscillations at cellular and subcellular levels using organisms expressing a transgene of a luminescence calcium indicator, the photoprotein aequorin. We will also isolate and characterize the expression patterns of clock genes. These studies will allow us to identify molecular components of the circadian biological clock.